Field of the Invention
The invention relates to a display device for a hybrid vehicle.
Description of the Background Art
In order to satisfy ever more demanding requirements for low noise emissions, low exhaust emissions, and low fuel consumption both now and in the future, carmakers are putting greater efforts into new vehicle concepts.
In these efforts, increasing use is being made of the concept of so-called hybrid vehicles. Hybrid vehicles are vehicles that are driven by more than one drive source; in current parlance, this is primarily thought of as the combination of an internal combustion engine and an electric machine that can be operated as an electric motor or multiple electric machines and the associated energy storage devices (fuel tank and traction battery). Apart from such a design of the hybrid vehicle, other combinations are of course also possible, for example the combination of a fuel cell and at least one electric machine.
In hybrid vehicles, the conventional tachometer frequently is replaced or augmented as a display device by a power meter, with which the driver command (load requirement) currently being drawn is displayed in different driving modes. The position of the power meter pointer here correlates more or less linearly with the gas pedal position selected by the driver.
Typical power meters are often designed as a circular instrument with multiple labeled scale graduations, from which the driver can read off different driving states.
For example, when the ignition is switched off, the pointer is in an “off” position. With the ignition turned on and in readiness for driving (but the driver is not depressing the gas pedal), the pointer moves to a “ready” position. If the driver applies slight to moderate throttle, the pointer moves between the “ready” position and a one hundred percent position. Frequently, a portion of this region is also graphically emphasized as a so-called “eco” region in order to deter the driver from excessive, high-fuel-consumption accelerations.
If the driver applies high to full throttle, then the electric machine in hybrid vehicles frequently assists the internal combustion engine temporarily as an electric motor. This is designated as the so-called “boost” mode. Since the total power achieved or total torque achieved is above the full load curve of the internal combustion engine, the power meter pointer is generally positioned above 100% of the power meter scale in this “boost” region.
In contrast, during braking the electric machine in hybrid vehicles operates as a generator and is used to charge the battery. This driving mode is likewise visually emphasized on the power meter as the “charge” region (the so-called regeneration region).
Moreover, a so-called “normal” mode and an “electric travel mode” (E mode) are frequently offered in hybrid vehicles. In normal mode, the division between driving with the electric motor (E driving) and driving with the internal combustion engine (ICE driving) is configured for minimum fuel consumption. Hence, electric driving takes place only at operating points where the efficiency of the internal combustion engine is poorer than the efficiency of electric driving including the charging and discharging efficiency of the traction battery. However, electric driving performance is restricted in certain respects by this approach.
By contrast, in E mode maximum electric driving performance is offered to the customer regardless of its influence on fuel consumption. The available torque and the available power at which a so-called “restart” can be initiated are thus significantly higher.
A restart can be understood to mean the driving state in which, following operation of the hybrid vehicle exclusively with the electric motor, the hybrid vehicle's internal combustion engine is again used additionally or exclusively as the drive source.
In hybrid vehicles, the driver may at times wish to keep the vehicle in the purely electric driving mode over a certain period, or in other words may wish to avoid restarting the internal combustion engine (which can be triggered by “stepping on the gas” too hard, for instance). However, this is comparatively difficult because of the relatively low power of the electric machine in hybrid vehicles as compared to the power of the internal combustion engine.
To this is added the fact that the load requirement (in particular the torque or power) at which restart is initiated depends on a very wide variety of boundary conditions, and thus is not always the same. When a high voltage (HV) battery is at a low temperature, for instance, the power of the traction battery is severely limited, causing the internal combustion engine to restart even for very low driver commands. As a general rule, purely electric driving is not possible at all below a certain battery temperature.
It is also necessary to take into account the fact that conventional hybrid batteries are typically operated in a state-of-charge window (SOC) between approximately 35% and 65% of their maximum charge state. If the charge state approaches the minimum permissible SOC, then restart is initiated even at relatively low power for reasons of operating strategy and battery physics.
All of the aforementioned effects thus have the result that the restart point is not constant within the display of the power meter and sometimes even changes successively during one electric driving phase.
In order to nevertheless provide the driver of a hybrid vehicle with a display device with which the driver can estimate when the internal combustion engine will be additionally switched on during electric-only travel, or in other words when a restart will take place, DE 10 2007 060 646 A1, which is incorporated herein by reference, proposes an additional display device. This additional display device serves to display the continually changing restart point, and can be provided as a trailing pointer or as a ring segment on the display area of the display device.
Against the background of the above remarks, it is nevertheless desirable to further improve the prior art display devices with regard to their informative value for the driver.